Tropical Depression ELEVEN

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TROPICAL DEPRESSION ELEVEN DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112013
500 AM AST MON SEP 30 2013
 
THE CONVECTIVE CLOUD SHIELD REMAINS SHEARED NORTHEAST THROUGH
SOUTHEAST OF THE CENTER. THERE HAS BEEN A NOTICEABLE INCREASE IN
LIGHTNING ACTIVITY DURING THE PAST COUPLE OF HOURS...WHICH IS OFTEN
INDICATIVE OF INCREASING VERTICAL WIND SHEAR. SATELLITE INTENSITY
ESTIMATES REMAIN T2.0/30 KT FROM TAFB AND SAB...ALTHOUGH SAB
REPORTED A DATA T-NUMBER OF T2.5/35 KT. ADT VALUES ARE T2.8/41 KT
AND A 02032Z OSCAT PASS CONTAINED SOME RAIN-FREE 30-35 KT WIND
VECTORS IN THE EASTERN QUADRANT...SUGGESTING THAT THE CYCLONE IS
VERY NEAR TROPICAL STORM STRENGTH. HOWEVER...GIVEN THE HISTORY OF
THIS SYSTEM GOING THROUGH SPORADIC CONVECTIVE BURSTING PHASES...THE
INTENSITY IS BEING MAINTAINED AT 30 KT WITH THE GUST DIFFERENTIAL
BEING INCREASED TO 45 KT UNTIL A MORE PERSISTENT CONVECTIVE PATTERN
BECOMES ESTABLISHED.
 
THE DEPRESSION HAS TURNED EASTWARD AND HAS SLOWED DOWN...AND THE
INITIAL MOTION IS NOW 090/04 KT. THERE IS NO SIGNIFICANT CHANGE TO
THE PREVIOUS FORECAST TRACK OR REASONING. THE NHC MODEL GUIDANCE
REMAINS IN GOOD AGREEMENT ON THE CYCLONE MAKING A SLOW CLOCKWISE
LOOP OVER THE NEXT 48-72 HOURS BEFORE ACCELERATING OFF TO THE
NORTHEAST OVER THE OPEN CENTRAL ATLANTIC AHEAD OF A BROAD
MID-/UPPER-LEVEL TROUGH ON DAYS 4 AND 5. THE FORECAST TRACK IS
SIMILAR TO THE PREVIOUS ADVISORY TRACK...AND LIES TO THE RIGHT OF
THE CONSENSUS MODEL TVCA AT 72 HOURS AND BEYOND DUE TO A
SIGNIFICANT WESTWARD BIAS CAUSED BY THE HWRF MODEL.
 
MOST OF THE INTENSITY MODEL GUIDANCE...AS WELL AS THE GLOBAL
MODELS...INDICATE THAT THE CYCLONE WILL REMAIN IN MODERATE SHEAR
CONDITIONS THROUGHOUT THE ENTIRE FORECAST CYCLE. THE EXCEPTION IS
BETWEEN 48 TO 72 HOURS WHEN THE SHEAR COULD LESSEN SOMEWHAT AS THE
CYCLONE BRIEFLY MOVES UNDERNEATH A NARROW UPPER-LEVEL RIDGE AS A
TROUGH BYPASSES THE SYSTEM TO THE NORTHEAST. THIS COULD ALLOW FOR
MORE STRENGTHENING BETWEEN THOSE TWO FORECAST TIME PERIODS BEFORE
SOUTHWESTERLY SHEAR BEGINS TO INCREASE AGAIN AT AROUND 72 HOURS AND
BEYOND. THE INTENSITY FORECAST IS CLOSE TO THE ICON CONSENSUS
MODEL...AND REMAINS NEAR THE LOW END OF THE GUIDANCE SUITE.

FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0900Z 26.9N  46.7W   30 KT  35 MPH
 12H  30/1800Z 26.9N  46.1W   35 KT  40 MPH
 24H  01/0600Z 26.6N  46.0W   35 KT  40 MPH
 36H  01/1800Z 26.4N  46.3W   40 KT  45 MPH
 48H  02/0600Z 26.3N  47.2W   40 KT  45 MPH
 72H  03/0600Z 27.4N  49.0W   40 KT  45 MPH
 96H  04/0600Z 29.5N  48.2W   35 KT  40 MPH
120H  05/0600Z 32.0N  44.7W   35 KT  40 MPH
 
$$
FORECASTER STEWART
 
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